1. Field of the Invention
This invention relates to electrical plugs, particularly electrical plugs which are useful for making an electrical connection between an elongate electrical cable and an electrical power outlet.
2. Introduction to the Invention
It is often necessary to make an electrical connection from an elongate cable such as a power cord, a grounded power lead, or heating cable to another elongate cable or to a source of electrical power such as a wall outlet. Connection to a power source is frequently made by means of an electrical plug. Connection of the cable to the plug often requires tedious and craft-sensitive assembly, as well as the use of special tools, in order to ensure that good electrical connection is achieved.
Elongate heating cables are one type of cable which often requires connection to a plug. Such heating cables are known for use in the freeze protection and temperature maintenance of pipes. Particularly useful elongate heating cables comprise (a) first and second elongate electrodes, (b) a plurality of resistive heating elements connected in parallel between said electrodes, e.g. a continuous strip of a conductive polymer in which the electrodes are embedded or which is wrapped around the electrodes, and (c) an insulating jacket which surrounds the electrodes and heating elements. In addition, the heating cable often also comprises a metallic grounding layer, in the form of a braid or a tape, surrounding the insulating jacket, which serves to electrically ground the heating cable and provides abrasion resistance. The heating cable may be cut to the appropriate length for use in each application, and connection must then be made to the plug.
Conventional electrical plugs for use with heating cables often require that, prior to installation of the cable into the plug, the conductive polymer must be stripped from the electrodes. Such an electrical plug is disclosed in U.S. Pat. Nos. 5,002,501 (Tucker) and 5,004,432 (Tucker), the disclosure of which is incorporated herein by reference. Stripping the polymer can be difficult, may require special tools, and may not result in completely "clean" electrodes, thus making good electrical connection to the plug difficult. In addition, the time required to strip the polymer and assemble the plug is relatively high. U.S. Pat. No. 5,252,081 (Hart) discloses a plug in which the electrode need not be stripped prior to insertion of the cable into the plug. Connection to the electrodes is made with conductive piercing means which penetrate the insulating jacket and the conductive polymer, thus contacting the electrodes. In order to make adequate contact, it is necessary that the piercing means, e.g. screws, be sufficiently tightened. In addition, it is important that the dimensional tolerance be precise to ensure that the screws directly contact the electrodes and maintain good electrical connection even after creep and/or aging of the polymer and electrodes.